1. Field of the Invention
The present invention relates to a polyethylene having a novel branching structure, and a method of production thereof. More specifically, the present invention relates to production of a polyethylene having a novel branching structure by polymerizing ethylene by employing a special catalyst system with superior polymerization activity. The polyethylene of the present invention is useful as inflation films, injection-molded articles, blow-molded articles, extrusion-coating materials, polymer blending materials, etc. in the same manner as conventional polyethylenes.
2. Description of the Related Art
Generally, polymerization of ethylene by a radical initiator at a very high temperature under a very high pressure gives a polyethylene having branched chains of length comparable with that of the main chain. On the other hand, polymerization of ethylene with a Ziegler-Natta catalyst under a low pressure gives a polyethylene having almost no branches.
For the purpose of producing a branched polyethylene by a method using a Ziegler-Natta catalyst, ethylene is copolymerized, generally with an .alpha.-olefin. The resulting polyethylene, however, does not have as long a branch as that of the polyethylene produced by radical polymerization.
In an attempt to produce a low-pressure polyethylene having such a long branched chain, ethylene is oligomerized, for example, by a nickel catalyst disclosed in Japanese Laid-Open Patent Application No. 63-12607 (1988), and the resultant oligomers are copolymerized with ethylene by a Cr catalyst. This method, however, does not gives a branch having a length comparable with that produced by a radical polymerization.